The present invention concerns a wheel-load sensor cast into a mass of material for positioning in a depression in a pavement or the like. The sensor includes a piezo-electric pickup. The pickup encloses an inner electrode and is enclosed in at least one outer electrode. The inner electrode is a solid conductor and the outer electrode a hollow conductor. The pickup is positioned in the pavement. The invention also concerns a method of manufacturing such a wheel-load sensor.
Wheel-load sensors of this type and methods of manufacturing them are known. The pickups are usually lengths of piezo-electric cable or strips of piezo-electric tape. The cable or tape encloses a solid conductor and is enclosed in a hollow conductor. The overall sensor is cast into a mass of material accommodated in a length of structural section open along one side.
Such sensors have drawbacks. When they are installed in the pavement and a vehicle drives over them it is impossible to prevent contamination of the results by undesirable horizontal load components. These components derive from the wheels of the test subject generating a forward horizontal thrust that extensively depends of the state of the road surface. The objects of the present invention are accordingly a wheel-load sensor and a method of manufacturing it that will minimize the contaminating horizontal components and ensure that the piezo-electric pickup's electronic output represents only the vertical components of the particular wheel load.